Semiconductor device and method of manufacturing the same

ABSTRACT

A semiconductor device comprises a bottom electrode, a top electrode, and a dielectric film provided between the bottom electrode and the top electrode and made of a perovskite type ferroelectrics containing Pb, Zr, Ti and O, the dielectric film comprising a first portion formed of a plurality of crystal grains partitioned by grain boundaries having a plurality of directions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority under35 U.S.C. § 120 from U.S. application Ser. No. 10/760,499, filed Jan.21, 2004, which is a Continuation Application of PCT Application No.PCT/JP03/06671, filed May 28, 2003, which was not published under PCTArticle 21 (2) in English, and under 35 U.S.C. § 119 from the priorJapanese Patent Application No. 2002-154585, filed May 28, 2002, theentire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method ofmanufacturing the same, particularly, to a semiconductor devicecomprising a capacitor using a ferroelectric material and a method ofmanufacturing the same.

2. Description of the Related Art

In recent years, the field of application of an LSI (large scaleintegrated circuit) is being expanded greatly. Specifically, the LSI wasapplied mainly in the past to, for example, a supercomputer, an EWS(Engineering Workstations) and a personal computer. However, the LSI isbeing mainly applied nowadays to, for example, a mobile apparatus and amulti-media system. As a result, it is important nowadays to impart anonvolatile function to the LSI, in addition to low power consumptionand high-speed operation. Also, it is important to introduce a newmaterial into the LSI in order to impart a higher performance and moremulti-functions to the LSI.

For example, a ferroelectric memory (ferroelectric RAM) with nonvolatility using a ferroelectric film, such as a film of a perovskitematerial or a film of a bismuth layered material, as an dielectric filmof a capacitor for storing information attracts great attentionrecently. The ferroelectric memory, which can be substituted for a flashmemory, an SRAM (Static RAM), and a DRAM (Dynamic RAM) and which can beapplied to a logic circuit embedded device, has high expectations as anext-generation memory. Also, since the ferroelectric memory can beoperated at high speed without using a battery, the ferroelectric memoryhas come to be used in a non-contact card such as an RF-ID (RadioFrequency-Identification).

The materials used for preparing a ferroelectric memory include highlyvolatile elements or elements which are diffused in the manufacturingprocess, and these react with other materials. As a result, themanufacturing process is greatly affected by the materials used forpreparing ferroelectric memories.

A PZT film, i.e., Pb(Zr, Ti)O₃ film, is one of the most typicalcomposite oxides used as a ferroelectric film. Lead (Pb) contained inthe PZT film has a higher vapor pressure than that of other elementscontained in the PZT film. Therefore, a method, in which an amorphousfilm is formed first at a low temperature, followed by applying a heattreatment at a high temperature to the amorphous film so as to convertthe amorphous film into a crystalline film, is generally employed forforming a PZT film. For example, widely employed is a method, in whichan amorphous PZT film is formed first at room temperature by employing,for example, a sputtering method, followed by applying an RTA (RapidThermal Annealing) treatment to the amorphous PZT film in the oxygenatmosphere so as to instantly crystallize the amorphous PZT film.

However, since it is difficult to control the Pb amount throughout themanufacturing process, it is very difficult to manufacture asemiconductor device with a high accurate repeatability at a high yield.It should also be noted that, in order to improve the reliability of thesemiconductor device, an oxide such as IrO₂, RuO₂, SRO (SrRuO₃), or LSCO((La, Sr)CoO₃) is used for forming the electrodes of the capacitor. Whatshould be noted is that these elements contained in the electrodematerial are diffused into the PZT film and react with Pb in grainboundary, resulting in degradation of I-V characteristics and poorferroelectric property.

Further, the amorphous PZT film was annealed in oxygen ambient in thecase of conventional crystallization. Hence, the crystals of the PZTfilm were exhibited a columnar structure as described herein later,resulting in the high leakage current and deterioration of switchingendurance.

The use of a PZT film is referred to in, for example, Jpn. Pat. Appln.KOKAI Publication No. 2000-156473 and U.S. Pat. No. 6,287,637B1. Each ofthese publications teaches that a PZT film formed first is annealed inan Ar gas atmosphere, followed by further annealing the PZT film in anoxygen gas atmosphere. However, the structure of the PZT film after theannealing treatment is not considered in each of these publications.Generally, it was difficult to obtain a ferroelectric capacitorexcellent in the leakage characteristics.

As described above, the leakage current was increased and the fatigueproperty was degraded in the conventional ferroelectric capacitor, whichmake it difficult to obtain a capacitor excellent in I-V characteristicsand reliability. Generally, it is of high importance to develop asemiconductor device comprising a capacitor of excellent characteristicsand reliability, and a method of manufacturing the semiconductor device.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda semiconductor device comprising: a bottom electrode; a top electrode;and a dielectric film provided between the bottom electrode and the topelectrode and made of a perovskite type ferroelectrics containing Pb,Zr, Ti and O, the dielectric film comprising a first portion formed of aplurality of crystal grains partitioned by grain boundaries having aplurality of directions.

According to a second aspect of the present invention, there is provideda method of manufacturing a semiconductor device, comprising: forming ona bottom electrode a dielectric film made of a perovskite typeferroelectrics containing Pb, Zr, Ti and O; and forming a top electrodeon the dielectric film, forming the dielectric film comprising: forminga first portion of the dielectric film on the bottom electrode by anannealing in an oxygen gas atmosphere; and forming a second portion ofthe dielectric film on the first portion by an annealing in an inert gasatmosphere.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a cross sectional view schematically showing the structure ofa capacitor according to a first embodiment of the present invention;

FIG. 2 is a cross sectional view schematically showing the structure ofa capacitor for a comparative example (conventional case);

FIG. 3 is a TEM image showing the cross sectional structure of thecapacitor according to the first embodiment of the present invention;

FIG. 4 is a TEM image showing the cross sectional structure of thecapacitor for the comparative example (conventional case);

FIG. 5 shows I-V characteristics of the capacitors according to theembodiments of the present invention;

FIG. 6 shows I-V characteristics of the capacitors for the comparativeexample (conventional case);

FIG. 7 relates to an embodiment of the present invention and shows theresult of analysis of Ru contained in a PZT film, the analysis beingperformed by using a TEM-EDX;

FIG. 8 relates to a comparative example (conventional case) and showsthe result of analysis of Ru contained in a PZT film, the analysis beingperformed by using a TEM-EDX;

FIG. 9 shows the result of an ICP analysis in respect of the dependenceon temperature of the Pb amount contained in a capacitor;

FIG. 10 shows the result of the measurement in respect of the fatigueproperty of a capacitor;

FIG. 11 shows the result of the measurement in respect of the imprintcharacteristics of a capacitor;

FIG. 12 is a cross sectional view schematically showing the structure ofa capacitor according to a second embodiment of the present invention;and

FIG. 13 is a cross sectional view schematically showing the structure ofa capacitor according to a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Some embodiments of the present invention will now be described withreference to the accompanying drawings.

First Embodiment

FIG. 1 schematically shows the structure of a capacitor in asemiconductor device according to a first embodiment of the presentinvention.

The capacitor shown in FIG. 1 is formed above a semiconductor substrate(not shown), such as a silicon substrate, and is used as a capacitor forstoring charges in a nonvolatile ferroelectric memory.

A method of manufacturing the capacitor shown in FIG. 1 will now bedescribed.

In the first step, a Pt film 11 is formed to a thickness of 100 nm by aDC magnetron sputtering method on an underlying film, such as an LP-TEOSoxide film. The sputtering treatment for forming the Pt film 11 isperformed in an Ar gas atmosphere for 20 seconds with the input powerset at 3 kW. Then, an SrRuO₃ film (SRO film) 12 is formed by a DCmagnetron sputtering method at room temperature. The sputteringtreatment for forming the SRO film 12 is performed in an Ar gasatmosphere for 11.5 seconds with the input power set at 700 W. Then, aheat treatment is applied at 550° C. to 600° C. for 30 seconds in anoxygen gas atmosphere so as to crystallize the SRO film 12.

In the next step, a PZT film 13, i.e., a Pb(Zr, Ti)O₃ film, is formed onthe SRO film 12. PZT is a perovskite type ferroelectric materialrepresented by ABO₃ and consisting Pb, Zr, Ti and O at least. Lead (Pb)corresponds to the site A element, and Zr or Ti corresponds to the siteB element. In some cases, a small amount of another element issubstituted in the site A element or the site B element.

The step of forming the PZT film 13 will now be described. In the firststep, an amorphous PZT film is deposited at room temperature on the SROfilm 12 by an RF magnetron sputtering method, followed by applying aheat treatment to the amorphous PZT film at 550 to 600° C. for 30seconds by an RTA treatment so as to crystallize the amorphous PZT film.Then, an additional amorphous PZT film is deposited on the crystallizedPZT film, followed by applying an RTA treatment to the additionalamorphous PZT film at 550 to 600° C. for 30 seconds so as to crystallizethe additional amorphous PZT film. As a result, formed is a crystallinePZT film 13 having a total thickness of 130 nm. As described above, thedeposition and annealing of the amorphous PZT film are repeated twice soas to decrease the surface roughness of the PZT film 13 and to makeuniform the Pb distribution in the PZT film 13. Incidentally, a highdensity target having a composition of, for example, (Pb_(1.15),La_(0.03))(Zr_(0.4), Ti_(0.6))O₃ is used as the PZT target. Also, thedeposition by the sputtering for forming each of the amorphous PZT filmsis performed in an Ar gas atmosphere for 72 seconds with the input powerset at 1.5 kW.

The annealing step of the PZT film 13 will now be described in detail.Concerning the lower layer PZT film (lower portion of the PZT film), theannealing is performed in an oxygen gas atmosphere for the former 15seconds after a temperature has reached the highest temperature of 550to 600° C., and the annealing is performed in an Ar gas atmosphere forthe latter 15 seconds. The switching from the oxygen gas to the Ar gasis carried out sequentially. On the other hand, concerning the upperlayer PZT film (upper portion of the PZT film), the annealing isperformed in an Ar gas atmosphere for the former 15 seconds after thetemperature has reached 550 to 600° C., and the annealing is performedin an oxygen gas atmosphere for the latter 15 seconds. The switchingfrom the Ar gas to the oxygen gas is carried out sequentially. A PZTfilm 13 b is obtained mainly in the annealing step of the lower layerPZT film carried out in the oxygen gas atmosphere, and a PZT film 13 ais obtained mainly in the subsequent steps.

In the next step, an SRO film 14 is formed to a thickness of 10 nm onthe PZT film 13, followed by forming a Pt film 15 to a thickness of 50nm on the SRO film 14. It should be noted that each of the SRO film 14and the Pt film 15 is formed by using, for example, a shadow mask, andis a circular pattern having a diameter of 160 μm. Then, a heattreatment is performed by using an electric furnace at 550 to 600° C.for one hour in an oxygen gas atmosphere.

As described above, obtained is a capacitor structure comprising abottom electrode including of the Pt film 11 and the SRO film 12, a topelectrode including of the SRO film 14 and the Pt film 15, and aferroelectric film of the PZT film 13 sandwiched between the bottomelectrode and the top electrode referred to above.

FIG. 2 schematically shows a capacitor structure for a comparative case.The Pt film 11, the SRO film 12, the SRO film 14 and the Pt film 15shown in FIG. 2 are formed by the methods similar to those employed forforming the Pt film 11, the SRO film 12, the SRO film 14 and the Pt film15 shown in FIG. 1. However, the annealing method employed for formingthe PZT film 13 shown in FIG. 2 differs from the method employed forforming the PZT film 13 shown in FIG. 1. The deposition and theannealing process of the amorphous PZT film are repeated twice in thecomparative case shown in FIG. 2, too. In the comparative case, however,the annealing process (RTA treatment) is performed each time at 550 to600° C. for 30 seconds in an oxygen gas atmosphere.

FIG. 3 shows a cross sectional structure of the capacitor according tothe first embodiment of the present invention shown in FIG. 1, which wasobserved by TEM (Transmission Electron Microscopy). Shown in FIG. 3 isthe structure before formation of the top electrode including an SROfilm and a Pt film.

In the PZT film 13 a obtained by the annealing method according to thefirst embodiment of the present invention, the crystal grain is shapedconical or oval. To be more specific, a cross section of the crystalgrain is wedge-shaped or shaped elliptical as shown in FIGS. 1 and 3.Because of the particular shape of the crystal grains, the directions ofthe grain boundaries are not aligned, i.e., the grain boundaries have aplurality of directions, and the directions of the grain boundaries arearranged at random. In other words, the grain boundaries are shapedzigzag between the lower surface and the upper surface of the PZT film.On the other hand, the crystal grains are shaped columnar in the PZTfilm 13 b, as in the PZT film 13 for the comparative case shown in FIG.2.

FIG. 4 shows a cross sectional structure of the capacitor for thecomparative case shown in FIG. 2, which was observed by the TEM. In thecomparative case, the crystal grains of the PZT film are shaped columnarand have an oblong (rectangular) cross sectional shape. Also, the grainboundaries are aligned and extend in a direction substantiallyperpendicular to the lower surface and the upper surface of the PZTfilm. In other words, the grain boundaries extend in one direction.

The electrical characteristics of the ferroelectric capacitor will nowbe described in respect of the capacitor according to the firstembodiment of the present invention and the capacitor for thecomparative case.

FIGS. 5 and 6 are graphs each showing the result of measurement of theleakage current characteristics (I-V characteristics). A curve(O₂—Ar/Ar—O₂) shown in FIG. 5 denotes the characteristics of thecapacitor according to the first embodiment of the present invention,and FIG. 6 shows the characteristics of the capacitor for thecomparative case (conventional case). In the comparative case shown inFIG. 6, the leakage current density is as high as 8.3×10⁻⁶ A/cm² at thevoltage of +2.5V. In the capacitor according to the first embodiment ofthe present invention, however, the leakage current density is as low as5.9×10⁻⁷ A/cm² at the voltage of +2.5V, supporting that the firstembodiment permits markedly improving the leakage currentcharacteristics.

In order to investigate the reasons for the experimental data given inFIGS. 5 and 6, the elements present in the grain boundaries of the PZTfilm were analyzed by a TEM-EDX. FIG. 7 shows the result in respect ofthe capacitor according to the first embodiment of the presentinvention, and FIG. 8 shows the result in respect of the capacitor forthe comparative case. In the comparative case shown in FIG. 8, prominentpeak for Ru is strongly detected in the grain boundaries of the PZTfilm. In the capacitor according to the first embodiment of the presentinvention, however, a prominent peak for Ru is not observed in the PZTfilm. One of the reasons for the phenomenon is that, since the firstembodiment of the present invention differs from the comparative case inthe shape of the crystal grain, as shown in FIGS. 3 and 4, the Rudiffusion vertical to the interface between PZT film and SRO film hasbeen changed. To be more specific, it is considered reasonable tounderstand that, since the grain boundary is shaped zigzag in the firstembodiment of the present invention, the effective diffusing length isrendered long, which suppresses the diffusion of Ru toward the surfaceof PZT film.

Another reason is considered to be as follows. FIG. 9 shows the resultof the ICP analysis in respect of the dependence on temperature of thePb amount. The ICP analysis was conducted by changing the type of RTAgas. As shown in FIG. 9, in the case of the RTA carried out in an oxygengas atmosphere, the Pb decreasing amount is small at temperaturesfalling within a range of between 300° C. and 700° C. In the case of theRTA carried out in an Ar gas atmosphere, however, the Pb amount israpidly decreased in the vicinity of the crystallizing temperature,resulting in reaching a Pb content close to the stoichiometric value.The experimental data given above support that, in the comparative case,a large amount of Pb or Pb compounds remain in the grain boundaries ofthe PZT film, and Ru is diffused and makes a reaction to form aconductive oxide represented by the chemical formula Pb₂Ru₂O_(7-x). Theconductive oxide thus formed is regarded as the cause of a leakage path.

It is considered reasonable to understand that the first embodiment ofthe present invention was rendered different from the comparative casein the leakage current characteristics under the situation describedabove. To reiterate, in the first embodiment of the present invention,the grain boundaries are shaped zigzag, resulting in suppressing the Rudiffusion vertical to the interface between PZT film and SRO film. Also,the Pb amount in PZT film is decreased by the RTA carried out in an Argas atmosphere. Such being the situation, it is considered reasonable tounderstand that the formation of the conductive oxide referred to aboveis suppressed to lower the leakage current.

FIG. 10 is a graph showing the result of measurement of the fatiguecharacteristics. In measuring the fatigue characteristics, the drivingvoltage at the switching polarization was set at ±6 V, the pulse widthwas set at 10μsecond, and the applied voltage in measuring thepolarization was set at ±4 V. In the comparative case (O₂/O₂), theamount of the remanent polarization begins to be decreased in thevicinity of 10⁵ to 10⁶ switching cycles. On the other hand, in the caseof the first embodiment of the present invention (O₂—Ar/Ar—O₂), theamount of the remanent polarization is not decreased even after 10¹⁰cycles of the polarization switching. It is considered reasonable tounderstand that, in the first embodiment of the present invention, thefilm is densified and the Pb amount is rendered optimum so as to producethe excellent effect described above.

FIG. 11 is a graph showing the result of the measurement of the imprintcharacteristics. After the heating at 150° C. for 600 hours or more, thevoltage shift relative to the initial value is decreased by about 0.1Vin the first embodiment of the present invention (O₂—Ar/Ar—O₂), comparedwith the comparative case (O₂/O₂), supporting that good imprintcharacteristics can be obtained in the first embodiment of the presentinvention.

As described above, in the first embodiment of the present invention,the amorphous PZT film is annealed in an Ar gas atmosphere, with theresult that, in the crystallized PZT film after the annealing treatment,it is possible to obtain dense and fine crystal grains, and the grainboundaries are rendered zigzag. Also, it is possible to control the Pbamount in the grain boundaries and in the interface. As a result, theamount of Pb contained in the PZT film is decreased, and the diffusionof Ru contained in the electrode is suppressed so as to make it possibleto markedly suppress the leakage current. In addition, the ratio of Pbin the interface between the PZT film and the electrode is made optimumso as to make it possible to improve the reliability of the capacitor.For example, it is possible to improve the fatigue characteristics.

Second Embodiment

FIG. 12 schematically shows the structure of a capacitor included in asemiconductor device according to a second embodiment of the presentinvention. The capacitor shown in FIG. 12 is substantially equal in thebasic structure to the capacitor according to the first embodiment ofthe present invention shown in FIG. 1, except that the second embodimentdiffers from the first embodiment in the structure of the PZT film.

A method of preparing the capacitor shown in FIG. 12 will now bedescribed. Incidentally, the second embodiment shown in FIG. 12 issubstantially equal to the first embodiment shown in FIG. 1 in thestructures and the methods of forming the Pt film 11, the SRO film 12,the SRO film 14 and the Pt film 15. Such being the situation, the methodof forming the PZT films 13 a and 13 b will now be described.

Each of the deposition and annealing processes of the amorphous PZT filmis repeated twice in the second embodiment, too, as in the firstembodiment of the present invention. The second embodiment is equal tothe first embodiment in the film-forming conditions, etc. for formingthe amorphous PZT film, but differs from the first embodiment in theannealing process (RTA process). Specifically, in the second embodimentof the present invention, the first layer amorphous PZT film isdeposited first, followed by annealing the deposited amorphous PZT filmin an Ar gas atmosphere so as to form the first layer PZT film 13 a. Onthe other hand, the second layer amorphous PZT film is deposited firston the first layer PZT film 13 a, followed by annealing the depositedamorphous PZT film in an oxygen gas atmosphere so as to form the secondlayer PZT film 13 b. In each of these annealing steps, the annealingtemperature is set at 550 to 600° C., and the annealing treatment iscarried out for 30 seconds.

Because of the method described above, the first layer PZT film 13 a forthe second embodiment is rendered equal in structure to the PZT film 13a for the first embodiment shown in FIG. 1. On the other hand, thesecond layer PZT film 13 b for the second embodiment is rendered equalin structure to the PZT film 13 for the comparative case shown in FIG.2.

The electric characteristics of the ferroelectric capacitor will now bedescribed in respect of the second embodiment of the present invention.

FIG. 5 referred to previously also shows the result of the measurementin respect of the leakage current characteristics (1-V characteristics).In the second embodiment of the present invention (Ar/O₂), the leakagecurrent density is as low as about 6.5×10⁻⁷ A/cm² at the voltage of+2.5V, supporting a marked improvement in the leakage currentcharacteristics. The effect described previously in conjunction with thefirst embodiment of the present invention is considered to contribute tothe improvement in the leakage current characteristics achieved in thesecond embodiment of the present invention.

FIG. 10 referred to previously also shows the result of the measurementin respect of the fatigue characteristics for the second embodiment ofthe present invention. In measuring the fatigue characteristics, thedriving voltage at the switching polarization was set at ±6 V, the pulsewidth was set at 10μ seconds, and the applied voltage in measuring thepolarization was set at ±4 V. In the second embodiment of the presentinvention (Ar/O₂), the amount of the remanent polarization is notdecreased even after 10¹⁰ cycles of the polarization switching. FIG. 10also shows the result of the measurement, covering the case where theprocess of forming the first layer PZT film and the process of formingthe second layer PZT film were reversed in respect of the annealingatmosphere, i.e., the case where the first layer PZT film was annealedin an oxygen gas atmosphere and the second layer PZT film was annealedin an Ar gas atmosphere (O₂/Ar). In this case, deterioration ofswitching endurance is brought about to some extent. It is consideredreasonable to understand that, since the amount of oxygen is renderedinsufficient in a region in the vicinity of the upper surface of thesecond layer PZT film because of the RTA treatment carried out in an Argas atmosphere, oxygen atoms contained in the SRO film were extracted bythe PZT film, which lowers the crystallinity of the SRO film, therebybringing about the deterioration referred to above. However, even in thecase of the O₂/Ar in respect of the annealing atmosphere, the secondlayer PZT film is rendered equal in structure to the PZT film 13 a inthe first embodiment of the present invention shown in FIG. 1, whichmakes it possible to improve the characteristics of the capacitor.

FIG. 11 referred to previously also shows the result of measurement ofthe imprint characteristics for the second embodiment of the presentinvention. Specifically, after the heating at 150° C. for 600 hours ormore, the voltage shift relative to the initial value is decreased byabout 0.1V in the second embodiment of the present invention (Ar/O₂),compared with the comparative case (O₂/O₂), supporting that good imprintcharacteristics can be obtained in the second embodiment of the presentinvention.

As described above, the second embodiment of the present invention alsomakes it possible to suppress the high leakage current and to improvethe ferroelectricity and the reliability of the capacitor, like thefirst embodiment of the present invention described previously.

Third Embodiment

FIG. 13 schematically shows the structure of a capacitor included in asemiconductor device according to a third embodiment of the presentinvention. The capacitor according to the third embodiment of thepresent invention is substantially equal in the basic structure to thecapacitor according to the first embodiment of the present inventionshown in FIG. 1, except that the third embodiment differs from the firstembodiment in the structure of the PZT film.

A method of preparing the capacitor shown in FIG. 13 will now bedescribed. Incidentally, the structures and the forming methods of thePt film 11, the SRO film 12, the SRO film 14 and the Pt film 15 shown inFIG. 13 are equal to those for the first embodiment of the presentinvention. Such being the situation, the method of forming the PZT films13 a, 13 b 1 and 13 b 2 will now be described.

In the third embodiment of the present invention, the steps ofdepositing and annealing the amorphous PZT film are repeated threetimes. The third embodiment is equal to the first embodiment in thefilm-forming conditions, etc. of the amorphous PZT film. However, thetime for forming each amorphous PZT film was set at 48 seconds in thethird embodiment so as to make the total thickness of the PZT film equalto that in the first embodiment. Specifically, in the third embodimentof the present invention, the first layer amorphous PZT film isdeposited first, followed by annealing the deposited amorphous PZT filmin an oxygen gas atmosphere so as to form the first layer PZT film 13 b1. Then, the second layer amorphous PZT film is deposited first on thefirst layer PZT film 13 b 1, followed by annealing the depositedamorphous PZT film in an Ar gas atmosphere so as to form the secondlayer PZT film 13 a. Further, the third layer amorphous PZT film isdeposited first on the second layer PZT film 13 a, followed by annealingthe deposited amorphous PZT film in an oxygen gas atmosphere so as toform the third layer PZT film 13 b 2. In each of these annealing steps,the annealing temperature is set at 550 to 600° C., and the annealingtreatment is carried out for 20 seconds.

Because of the method described above, the second layer PZT film 13 a isrendered equal in structure to the PZT film 13 a for the firstembodiment of the present invention shown in FIG. 1. Also, each of thefirst layer PZT film 13 b 1 and the third layer PZT film 13 b 2 isrendered equal in structure to the PZT film 13 for the comparative caseshown in FIG. 2.

As described above, the third embodiment of the present invention alsomakes it possible to suppress the high leakage current, to improve thefatigue characteristics, and to improve the characteristics and thereliability of the capacitor, like the first embodiment of the presentinvention described previously.

In the third embodiment of the present invention described above, theprocess of depositing and annealing the amorphous PZT film is repeatedthree times. Alternatively, it is also possible to deposit first anamorphous PZT film, followed by successively applying an annealingtreatment in an oxygen gas atmosphere, an annealing treatment in an Argas atmosphere and, then, an annealing treatment in an oxygen atmosphereto the amorphous PZT film. It is possible to obtain the structure shownin FIG. 13 in this case, too. It is also possible to obtain thestructure as shown in FIG. 13 by changing, for example, the annealingconditions even in the case of employing the process employed in thefirst embodiment of the present invention described previously.

Each of the embodiments described above does not comprise the BEOL (BackEnd Of the Line) process, such as forming a contact, a wiring and aninterlayer film, etching, and polishing for planarization. However, itis possible to obtain the effects described above even in the case ofemploying the full process. Also, in each of the embodiments describedabove, the amorphous PZT film, etc. was formed by the sputtering method.However, it is of course possible to employ another film-formingtechnique.

Also, in the case of manufacturing a memory device having a COP(Capacitor On Plug) structure by using, for example, polycrystallinesilicon (polysilicon) or tungsten as the plug material, it is possibleto suppress the diffusion of oxidizing agent to the plug surface byemploying the method for each of the embodiments described above, whichmakes it possible to realize a semiconductor memory device of a largerscale of integration.

Further, in each of the embodiments described above, it is desirable forthe annealing temperature T1 for annealing the lower layer side SRO film12, the annealing temperature T2 for annealing the PZT film 13, and theannealing temperature T3 for annealing the upper layer side SRO film 14to have the relationship of: T1≧T2≧T3. Also, concerning the PZT film 13,it is desirable for the annealing temperature for annealing the upperlayer side not to be higher than the annealing temperature for annealingthe lower layer side.

Still further, in each of the embodiments described above, it ispossible to use a He gas, a Ne gas, a Kr gas, a Xe gas, a Rn gas or anitrogen gas as an inert gas in place of the Ar gas for carrying out theannealing treatment.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A method of manufacturing a semiconductor device, comprising: forminga bottom electrode above a semiconductor substrate; forming a lowerdielectric film, which is made of perovskite type ferroelectricscontaining Pb, Zr, Ti and O, on the bottom electrode; annealing thelower dielectric film in an oxygen gas atmosphere; forming an upperdielectric film, which is made of perovskite type ferroelectricscontaining Pb, Zr, Ti and O, on the lower dielectric film; annealing theupper dielectric film in an inert gas atmosphere; and forming a topelectrode above the upper dielectric film.
 2. The method ofmanufacturing a semiconductor device according to claim 1, wherein atleast one of the bottom electrode and the top electrode includes a filmcontaining Ru.
 3. The method of manufacturing a semiconductor deviceaccording to claim 1, wherein the inert gas includes at least one of aHe gas, a Ne gas, an Ar gas, a Kr gas, a Xe gas, a Rn gas, and anitrogen gas.
 4. The method of manufacturing a semiconductor deviceaccording to claim 1, further comprising: forming an additionaldielectric film, which is made of perovskite type ferroelectricscontaining Pb, Zr, Ti and O, on the upper dielectric film; and annealingthe additional dielectric film in an oxygen gas atmosphere.